An ASIC implementation of a sub-band filter bank

Sub-band filtering is a frequency domain technique using linear filters to separate a finite duration sequence into a set of frequency bands. The technique can be used to decorrelate an image into a number of `sub´-images, representing different frequency bands within the original image spectrum. Each frequency band can then be quantised according to its perceived importance in the original image. Transform coders, such as the DCT provide a similar function, but are complex and hence are applied to an image on a block-by-block basis. In contrast, sub-band filtering is separable and can be applied to the full image directly. The amount of decorrelation between sub-bands is adjustable, and if sharp roll-off filters are used, sub-band filtering gives improved frequency separation and hence better decorrelation when compared to transform methods